Variable range signal generating circuit with means for computing initial velocity



April 29, 1958 L. D. BALL r-.TAL 2,832,537

VARIABLE RANGE SIGNAL GENERATING; CIRCUIT WITH MEANS FCR COMPUTING INITIAL VELOCITY Filed March '7. 1955 2 Sheets-Sheet. 1

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VARIABLE RANGE SIGNAL GENERATING CIRCUIT WITH MEANS FOR COMPUTING INITIAL VELOCITY Filed March 7, 1955 2 Sheets-Sheet 2 United Staates Parent-O VARIABLE RANGE SIGNAL GENERATING CIR- CUIT WITH MEANS FOR COMPUTING INITIAL VELOCITY Lloyd David Ball, Los Angeles, Brooks E. Cowart, Pacoima, and George Bruer Crane, Redondo Beach, Calif., assignors to Gillillan Bros. Inc., Los Angeles, Calif., a corporation of California Application March 7, 1955, Serial No. 492,482 Claims. (Cl. 23S-61.5)

This invention relates to a variable range signal generating circuit with means for computing initial velocity and, more particularly, to a `circuit for producing a varying range signal as a function of the integral of velocity, where the velocity is computed on the basis of an initial condition plus the integral of any velocity changes resulting thereafter.

Although the present invention has a multitude of applications, it is particularly applicable to a ground controlled approach system of the general type described and claimed in copending U. S. patent application Serial No. 492,627 by Lloyd David Ball et al. for Velocity Tracking System for Increasing the Range of Acquisition of Moving Targets, filed March 7, 1955. In this system the present invention forms part of a feedback loop which automatically corrects errors in a target range calculation. The invention is utilized in the system to produce a range signal which controls the function of a time-modulator circuit. The time-modulator circuit delays applied system trigger signals to produce range pulses after a time intervalV corresponding to the amplitude of the controlling range signal. The delayed range pulses thusy produced are compared withY actual target echoes in order to determine whether the computed range is greater or smaller than the actual target range. The system includes means for generating early and late signals indicating the sense and/magnitude of the difference between the actual target range and the computed target range. These signals are combined to form an error signal whichV is utilized in the range signal generator of the present invention to indicate changesl in target velocity.Y

According to the basic approach of the present invention, the range calculation is initiated by forming an initial velocity signal as a function of a predetermined range difference divided by a time interval difference, the range difference being specified by first and secondrange marking signals. The initial velocity signal thus formed is modied in an error signal integrator in accordance with subsequent changes in target velocity, the error signal integrator producing a velocity output signal based upon the computed inital velocity and any changes which may result thereafter. The velocity output signal is then integrated from an initial range condition in orderV to form a varying range signal. In thismanner a range signal is generated as the function of target velocity, where the target velocity includes an initial velocity Ycondition plus any velocity changes resulting thereafter.

In its basic structural form the invention comprises a sequence control circuit responsive to 'target acquisition signals for producing sequencing signals indicating the times of passage of the target through predetermined; first and second ranges. The sequencing signals are utilized to actuate an initial velocity computer to produce an initial velocity signal representing the average velocity of the target between the first and second ranges. yThe sequencing signals are also utilized to transfer the initial velocity signal to` an-error signal integrator. The error signal integrator further receives error signals or velocit-y` change signals and is operative to produce -a varying velocity signal representing the target velocity after the second range.

The varying Velocity signal is applied. to a velocity integrator circuit whch also receives initial condition signals from an initial range-setting circuit controlled by the sequence control circuit. The velocity integrator is then operative to produce a varying range signal vas a function of the varying velocity signal produced by the error signal integrator; the constant of integration being an initial range condition signal produced Aby the rangesetting circuit, corresponding to the second range. y

The basic means of the invention described above may be considered as arrangeable into several groups. For example, portions of the sequencing circuit may be considered to form parts of the other circuits according toy the` particular function which is performed. Thus the initial velocity computer and the corresponding control' section of the sequencing circuit may be consideredto be a' means responsive to the first and second acquisition signals for producing an initial velocity signal. In a similar manner the velocity integrator, initial range setting circuit, and corresponding sequencing control circuits may be considered to form anintegral means responsive to the acquisition signals and to the varying velocity signal produced by the error signal integrator for producing a varying range signal. Other basic arrangements will become apparent from the description and claims whichV follow. Y

In a more specific form of the invention, the initial velocity computer includes a rectangular hyperbolic function generator for producing an'initial velocity signal v defined by the function v.t=Ad, where t represents an; independent time variable and Ad a distance differencel which is assumed to be a constant. In operation the initial velocity computer may be assumed to generate theyhyperbolic function from a time t'=t0 until a time t=t1, where the conditions t'=t0 and t=t1 corresponds to the times the target crosses the iirst and second range marks, respectively. In this manner the velocity signal v is effectively produced as the function V=Ad/`(0-l) where Ad is the range difference between the ranges specified by the rst and second marks and At is the time interval between t0 and t1. Y

Although many forms of hyperbolic function generators areavailable which may be employed by the prescuits are utilized, the desired hyperbolic function `being derivable therefrom in a unique manner. v

Certain circuits in the initial velocity computer'talso form part of the error signal generator and are first operativein producing the velocity signal of the hyperbolic function and then operative in an integratingl constant capacity. Thus Where the error signal integrator includes a- D. @amplifier and integrating capacitor, the integrati. ing capacitor also forms partof the initial velt'acitytio'rn-- puter. In this manner the same capacitor Vchargingfcircuit may beutilized-to generate the rectangularhyperbolic function, where thecapacitor is utilized inl one off the exponentialcharging circuits, and then is utilized asf the integrating capacitor where its initilcliarge formed during the previous operation corresponds to 'initialvef locity-t f I u t1 The technique of utilizin'gfthesame: circuit; elements V various points in Y the v circuit of for initial 'condition computation and subsequentV integration from the computed initial condition as a constant of integration may have general applicability in theV field 'Y of analog computing. Thus this feature of the invention is not limited to utilization in a range signal generator application and is claimed hereinvas an important `subcombinational contribution. f i

Accordingly, it is i l to providev a range signal generating circuit for producing a varia-ble range signal as a function of the integral ,y Y of target velocity.`

, produced Yin accordance withvelocity changes or errors.

A furtherf'object'is toprovide an initialvelocity computer forAv indicating the average target velocity between first ,and` second range marking signals indicating the Vtimes that aV target passesthrough corresponding ranges.

Still'another object of the invention is to provide a Vcircuit for computing initial target velocity in response Yto applied target acquisition signals indicating the' time of y'passageof atar'get throu'ghpredetermined first andr second' ranges,v the velocity being determined as a'rec-` tangular hyperbolicfunction v.t=Ad. Y

Yet a further object of the invention is toprovide Va signal generator circuit for producing a variable range signal in accordance with :the .integral of a computed ini-y in velocity occurring thereafter. Y

Y,Still a further object is to provide a circuit for inte-V grating from a computed )initial condition introduced before theintegrationV to p rovide an integrating constant;V

the element utilized to receive the initial condition in the preintegration operation being Valso` utilized inthe integration operation. Y l V a `The novel features which are believed to be characteristic ofthe invention, both as toitsporganization and *Y method of operation, .together 'with further/objects and Vadvantages theerof, will be better understood from the an object ofthe present invention tial target velocity as modified bylany errors or changes' a' f The varying velocity signal produced by circuit 300 is appliedto a velocity integrator 400 which also receives initial condition signals produced by an initial rangesetting circuit 5ll0controlledby Vcircuit 100.

WhileVv sequencing control circuit 100 has been s hown as a separate device, it will be understood that it is separable into a plurality of circuits corresponding to itsyari.- 1

ousjfunctions, each of the separated circuits thenbeing considered to form part of the Ymeans controlled. Thus the section of circuit 100 which controls the sequencing of initial velocity computer circuit 200 may be considered to form party of that means forming a device for com' puting initial target velocity in responsertoapplied` acquisition signals. This subcombination, it may be noted,

is considered as part of the present invention and claimed Y l as such.

, In asimilar manner part may be considered to be associated vwith -velocity integrator 400 or with initial range setting circuit 500, veachV means vresponsive to applied acquisi-v forming'a separate tion signals.

The general functional definition of the basic compo-4 nents of the invention may; beV better understood by con-` sidering the waveforms of Fig. la illustrating atypical operation. Y

As indicated in Fig. la, thesystem ofthe invention may be considered to function during threej basic periods` of operation. At the outset the system is ina preacquisition period before a target crosses a first range mark in-I dicated by a corresponding range signal'.V The seconde period is initiated when the target crosses the Vfirst range mark and an acquisition signalV is produced indicating following description considered in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose. of

illustration and description only, and are not 'intended as a definition of thelimits of the invention. p, Fig. l is a block diagram ofy the basicgembodiment of Y a variablev range signal generatingY circuit, Yaccording to.

the present invention; w Y V l f Fig. la is'a composite set of waveforms appearing at Fig. 1 during a-typical operation; f f

Fig. 2 is a schematic diagram of a speciicform of theV invention utilizing ,one species` of the rectangular hyperbolic function generator.V

Reference is now made to Fig. l wherein'the basic embodiment of the present invention is shown in block diagram form. As shown Vin Fig. 1,(the basic embodirnent compirses aV sequence'control circuit 100 for lren' ceiving applied target acquisition signals and for producing sequencing signals indicating Vthe times of passageV YYof a target through predeterminedrst and second ranges.l

The sequencing signals; produced ibycireuit 100 ,are VutiL lizedto` initiate the operation of an initial velocity comj puter200Y providing an initial velocity signal represent-v f ingthe average velocity of the target between therst and Y Vsecond ranges. Y

The sequencing `signals produced by circuiti-1100 are also utilized to control the transferof the initial velocity signal tojan error integrator 390 which further receives applied error signals' or velocity change signals.r lCircuit'30ll is'responsive to the applied input signals tofpro-Y 'Y duce a Yvarying velocity signal representing the target Y velocity afterthe second range. 1 L

the lcorresponding time of occurrence. This second period f Vis designated asV an acquisition period since it is during this period that an initial target velocity Vsignalis acquired providing vsignal informationl for continuously trackingv the target during the third or tracking period.

It will be noted in Fig. la that theV range signal produced by the system is initially set to a iirstvalue representing the rst range mark and Yis theny stepped to a second value representing a second range mark upon receipt of a iirstacquisition signal A1 'marking the time the target crosses theirst range mark. VThe first acquisition signal A1 `also iactuates velocity computer 200 to produce the signal v as theratio of the range difference Aad divided the independentvariable'tyrepresenting time.

`'The time that the first acquisition signal isproducedr considered to be Yt0 and marks the beginning of a time dif.-V

fjerencerinterval At which lis terminated upon receipt of a a i second acquisition signalfAZV markinggthe time `t1 that the Y target passes a second range mark.

. -The receipt'of the second acquisition signal A2,"then,

.terminates the hyperbolic function generatingoperation of the initial velocity computer and causes Y,the sequencing circuit to signal the beginning of the target velocity tracking period. During this'period the initial velocity signal previously computed is integrated to fonn a varying range signal and is moditiedby adding error signals thereto to compensateffor errors in initial velocity computation or target velocity changes;

While the invention provldes a Ygeneral technique for range .-signal generating through initial velocity computai R114, the signalV tion and integration and is not limited to specific forms of circuits, one specic form of the invention isv shown in Fig. 2 in order to illustrate an operable embodiment. Y 5 Referring now to Fig. 2, it is noted that acquisition signals Aapplied to sequence control circuit k arereceived by an amplifier stage including a vacuum tubel Illlreceiving B+ potential through'a load resistor R111v and having its cathodecoupled ,through a cathodeload resistor R112fandra capacitor C113 connected nkpar'allel to a resistor R113 to ground. The acquisition signals are `applied to thegrid ofv tube T111fthrougl1 an input resistor being developed acrossr a Vload resistor" ofvsequencingV circuit 100 Y f When acquisition signal A1 is feceived by amplifier 110, capacitor C113 is rapidly charged to the peak value thereof and slowly discharges through resistor R113. This provides `a sustained output signal which is effective throughja resistor R121 to actuate a tube T120 to supply current to a relay Rto through a current-limiting resistor R122. The current path of relay Rio is completed to ground through a reset switch W.

Thus acquisition signal A1 is effective to actuate relay Rzo and transfer all corresponding contacts thereof; the transfer of relay Ro-1 removing a 28 volt potential applied through a resistor R131 to the grid of a tube T130. The 28 volt potential is transferred to provide holding current for relay Rto. In this manner, relay Rto is actuated and held until subsequent release and tube'T130, receiving anode potential through a load resistor R132, is changed from a normal highly-conducting condition with a resulting low impedance to ground, t'o a condition of low V conductivity with high impedance to ground.

It will `be noted that the grid of tube T130 is also connected to a voltage-retaining circuit 140 which is operative to retain the 28 volts previously providedthrough contact Rt0-1 for a predetermined time interval to maintain the highconducting condition of tube T130 until the end of this predetermined time interval. This time interval is selected on the basis of information indicating the minimum time interval to be expected between acquisition signals A1 and A2.

After tube T130 is in a condition providing a high impedance to ground a gating circuit is effectively opened for acquisition signal A2 which may then pass through resistor 132 to a tube T150 supplying current through a resistor R151 to a relay Rtl. The current path for relay Ril, it will be noted, may also be interrupted by actuating switch W providing a ground connection therefor.

When relay Rtl is actuated in response to acquisition signal A2 contact Rtlv-l is transferred providing a holding circuit so that the relay remains in an actuated condition until subsequent release by opening contact W. In addi-y tion contact R13-2 in amplifier circuit 110 is transferred to provide a ground connection for the grid of tube T111 preventing the further passage of acquisition signals.

Thus acquisition signal A1 is effective to actuate relay Rtl which is then held and provides a switching'function for opening agate for acquisition signal A2 after the predetermined interval determined by the time constant of circuit 140.' And, when signal A2 is received and held a switching function is performed which prevents further actuation of relays Rt.

The switching signals provided by relays Ro and Rtl in circuit 100 are utilized to .control the operation of initial velocitycomputing and initial range setting circuits 200 and 500. It may be noted that the term signal as utilized herein .may specify either a relay switching operation or an electrical signal since it is conceivable that the switch function provided by circuit 100 may be effected without relay circuits through the utilization of electronic switching signals.` Therefore, the term signal is intended to include a mechanical function as well as an electrical function.

- Referring specifically to the initial velocity computer 200, it will be noted that prior to actuation of relay Rzl contact Ril-3 remains unactuated and completes a resistance feedback path for a chopper stabilized D. C. amplifier stage 310 through a resistor'R201. Suitable types of chopper-stabilized D. C. amplifiers are wellfknown .in the art, typical circuits being shown and described, for example, on pages 200 through 210 of a book entitled Electric Analog Computers, published in 1952, by Korn and Korn; New York and. London.

It will also be noted that circuit 200 includes an integrating ,capacitor C202 which forms part of an integrating feedback loop for amplifier 310 after relay Rtl is actuated. Integrating capacitor C202 also forms part of a hyperbolic Vfunction generating circuit 220 which is inop- Y circuit 210 in the manner described above.

erative prior to the actuation' of relay Rt. The circuit connections of the hyperbolic function generating circuit- 220 exist after relay Rt() has been 4actuated andall corresponding relay contacts have transferred. Thus irf will; be noted that capacitor C202 is connected'to one end of a resistor R202 having its other end connected to ground.: This connection forms a first'RC exponential circuit 202.` An output signal is derived from the junction of .capacitor C202 and resistor R202 and is` applied to a second exponential RC `circuit 203 comprising a resistor R203 and ay capacitor C203. The two exponential charging circuitsv are designed according to the principles introduced in the. above-mentioned copending application by Cowart et al. for Function Generating Circuits Requiring Only Linear" Elements. i

Prior to the actuation of relay Rto, capacitor C203 isk in operation then, circuit 200 essentially provides a.V Y

resistive feedback circuit for amplifier 310 whichresults in a predetermined potentialv being applied to one terminal of capacitor C202. TheV potential applied to the other terr. minal of capacitor C202 is provided by initial charging The status of. circuit 200 at this point corresponds to a preacquisitio condition.

As s-oon as the lfirst acquisition signal A1 is received and relay Rto is actuated, hyperbolic function generating circuit 220 goes into yoperation and generates the velocity signal v as a function of a fixed range difference over variable time. This signal is generated as a varying chargev across capacitor C202 so that at the end of the acquisition` -period upon actuation of relay Rtl capacitor C202 is en.

tered intothe feedback circuit `of D. C. amplifier 310 with an initial charge corresponding to the computed initial velocity formulated as an average velocity equal to Ad/At, where Ad is the range difference established and At equals IHU.

The switching signals provided by relays RID and Rtl are also utilized to control range setting circuit 500. Initially circuit 500 provides a range signal for chopper-stabilized' D. C. amplifier stage 410 corresponding to the first range mark. During this time circuit 500 also provides a resistance feedback for D. C. amplifier 410 through a resistor R510 connected in parallel to a transient bypass capacitor C510. Thus initially D. C. amplifier 410 provides a constant amplification function generating the first range signal. The value of this first range signal may be adjusted through a range adjust potentiometer P520V i coupled toV resistor R510 by a resistor R521.

introducing a range step signal. The range step signal may bevaried by adjustinga variable resistor R530 forming a voltage divider with series connected resistor R531; the junction of the two resistors provides a range step signal when relay contact Ro-4 is closed providing a ground connection, the signal being applied to the input circuit of amplifier 410 through an adding resistor R532 and normally closed contact Rt1-5.

Thus when relay Rr is actuated the input signal magnitude for amplifier 410 is stepped, resulting in a corresponding range signal step at the output circuit of the amplifier. This `stepped range signal charges in integrating capacitor C540 to an initial value representing the second range mark through normally closed contact RII-6. When re,- lay Ril is actuated contact Rtl-istransferred completing operation.

a' feedback path for capacitor-.C540 to the inputV circuit of amplifier 410. n t 4 vIt willbe noted that a variable voltage-dividerfcircurt 311`is shovv'nY coupled to amplifier 310 and may be con-V sidered to form part of the output circuit thereof. Variablevoltage dividercircuit 311 allows a scalefacto1 to Y be introduced into theivelocitysig'nal applied to amplifier Y410 through transferred 'contact'Rtl-d The specific operation of the embodiment of 2 should now bereadily understood.' Acquisition signal Y A1 is effective through arnplifierstageV V110 and tube T120 to actuate' relay Rto. Y The actuation of relay Rt@ provides switching operationswhich initiate-theoperation-of hyperbolicfunction generating circuit 210, froincertain Y ,previouslyV established signal conditions, and Ywluch step i, the rangesignal provided by circuit500 from an'. initial value representing the first range niark to a steppedr value representing the' second range mark. The stepped signal Y is utilized toV provide an initial range lsignal across integrating capacitor C540.V

' The; actuation of relay'Rto also opens an effectivefgate responsive V to saidacquisition signals for establishing'an initial jrange condition representing said second -range and for integrating saidv varying velocity signal froni'said initial range condition to form a varying range signal.- 2; A circuitfor .producing a target rangesignal asV the Y integral oflt'arget velocity from an initial velocity cong for producingY a` varying velocity signal'represe'nting the* i -w afterJa time interval determined by circuit 140, allowing Y theipassage of acquisition signal A2 throughrtube` T150 to actuate relay Ril. This` causes a switching function which prevents further acquisition signals Yfrom being effective."V I Y, v

j Y wThe actuation ofrelay Rtl closes .the integrating feedback loops for amplifiers 310 and 410; integrating capaci- Vto r.C20'2 completing the loopfor amplifier 310 and providing an initial velocity signalrcomputedin circuit 210 asfthefunction Ad/At, and integrating capacitor C540- Y completes the loop for amplier 410' and providesan Vinitial rangeV signal corresponding to the second range mark. The switching of relay Rtl'also completes a connection between amplifiers 310 and 410 throughY suitable scale factor providing means; Y Y

From the foregoing descriptionit should now be apparent that the present `invention provides avariable range Vsignal generating circuit with means for computing initial velocity, thev circuit being particularly useful in velocityv tracking systems for increasing the range of acquisition ofprnoving targets. 'Y Y Y It should `now' be apparent that the invention may also bev considered as providing aV novel land useful initial velocity computer, forming a subcombinational part of the range signal generating circuit. Theinitial velocity computingV circuit may be considered4 as including rthe l necessary switching circuits in circuit 100, for providing Y 'switching to obtain initial signals 'for the hyperbolic- `function circuit'210 and switching for providing an output vsignaljrepresenting the nal charge of integrating capacitor CEZ.

- Another important subcombinational aspect which has beenprovided is the arrangement'whereby aninitial con- Vdition may be computed and ythen transferred to an 'fiutegrating circuit, where thecircuit element providingra stored representation of the initial condition during com-- -putation is also utilized subsequently in the integrating `What isV claimed is:7777 Y Y i f Lulnatarg'et tracking systemtwhere the range of a target is to be computed as, a function of the integral lof vtarget'velocity-fromanfinitial velocity condition computedrbetween'tfirst and second ranges, the time of passage :of thetargetV throughrthe: first and second ranges kbeing signaledrbyprst and second acquisition signals,

respectively; the combination comprising: first means responsive Vto the acquisition' signals and to input signals representing any error for change in targetLvelocity. for producing a varying velocity signal, said first means'including a vfirst circuit forY producingan initial velocity y. signal anda second circuit for receiving the initial velocity signal and any error signals to produce the varying velocity signal as a functionrof the initial velocity signal and the integral of the error signals; and second means dition computed; between first and second'acqusitionsig nals indicating the timesk that the target passes through corresponding first andsecond ranges, the'jvariationsV 'in the initial velocity condition being indicated` by a varying, error signal, said circtlitfcomprising: an initial Velocity computer responsive Yto said Vfirst and second acquisition signals for producing an initial'v'elocity signaltrep Y r'esenting the averagevelocity'of thev target between .the`

first and'second ranges; anerror signal integrator respon;V

sive toY said'initial velocity signaland tothe, error signals target velocity after the second range; avelocity" integratingcircuit responsive to said velocityV signal for producingra varying range signal as the integral of said varying velocity signal; an initial range setting circuit forV .Y

initially establishing a signal condition sin said velocity integrator representing saidsecond range; and a sequence control 4.circuit for actuatingr said initial Yvelocity computer andsaid initial range 'setting circuit to operate in the proper sequence. f v

3. A range computer for producing l'an output signal representing the varyingrange of atargetas a functionk Yof theii'ntegra'l ofthe target velocity,v theV integral including an initial Velocity condition correspondingtojthe f average target velocityV between first and second range marks represented byfcorresponding first and second .sig-T 4. In atargettracking system'where a variable .rangeV signal is to be computed as a function ofthe integralof target'velocity from an initial velocity condition, an initial velocity computer comprising: 'an' input 'circuit fory receiving 'first and second acquisition signals indicating the time of passage of the targetthrough `firstand lsecond ranges, said input Vcircuit producing corresponding'ifirst and second sequencing signals; a reciprocal function generating circuit actuable to produce a'varying signalv as a function of arange difference Yfactor corresponding to therange between vsaid first and second ranges, and as a. function ofthe time difference'following the occurrence of'said first acquisition signal; rst means respo'nsive to said first acquisitionV signal for actuating'said reciprocal function generating jcircuitlto initiate said Yvary'- 1 ing signal v; and second means responsive to said-second aequisitionsignal for controlling the termination .of .operlation of said reciprocal function generating circuit,V the 1 final signal of said function generating circuit representing Vthe initial velocity condition. f 5. The initial velocity computer defined inclaim 4 Y Ywherein said first and second sequencing signals are'relay switching signals; wherein said first means includesa first relay device responsive to said first sequencing sig- 'n nal for initiating said reciprocalV function generating op- Y eration; and wherein said second means includes a secondV relay device responsive to said secondrseq'uen'cing signalv Y for terminat'ng said Yreciprocal function generating operaf tion. 6. A circuit correspondl v for producing output signal'represent-` ing an initial velocity condition determinedas vthe average 9 target velocity between the occurrence of first and second control signals representing the times that the target passes through first and second ranges, respectively, said circuit comprising: a function generator actuable to produce signal v defined by the function v.t=Ad, where the value of the signal v at the termination of operation of CFI said function generator corresponds to the initial velocity condition, t is an independent variable representing time after thel occurrence of the first control signal, and d is the range difference between said first and second ranges; a first control circuit coupled to said function generator responsive to the first control signal for actuating said function generator to produce said signal v; and a second control circuit coupled to said function generator responsive to the second control signal for terminating operation of said function generator.

7. The circuit defined in claim 6 wherein said function generator includes two resistance-capacitance exponential circuits coupled to provide an approximate simulation of said rectangular hyperbolic function.

8. A circuit for integrating an input signal from a precomputed constant, said circuit comprising: first means actuable to compute said constant, said first means including a capacitor which may be switched out thereof upon termination of the computing of said constant; second means actuable to integrate the input signal from an initial condition represented by said constant, said second means having an integrating feedback circuit including said capacitor, after the switching of said capacitor out of said first means; and third means coupled to said rst and second means for actuating said first means to compute said constant, and for providing the switching of said capacitor to said second means.

9. The circuit defined in claim 8 wherein said first means is a hyperbolic function generator actuable to produce a signal v across said capacitor, the signal v-being' K defined by the function: v=Ad/t, where Ad is a constant va constant over time, where the constant is determined by the difference between said first and second marks; second means for receiving said reciprocal signal and for storing'the instantaneous value of said reciprocal signal; and third means responsive to said second input signal for terminating the operation of said first means, the final stored value of said second means representing the initial velocity of the targetr through the first and secondk marks.

References Cited in the file of this patentV UNITED STATES PATENTS Tull et al July 25, 1950 MacNichol et al. Jan. 27, 1953 

